best sub for spendor S8r


I would like some recommendations for subs that go well with my Spendor. S8e's...price can be up to about 2K used
auralone
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REL. Nothing in my pretty substantial experience intgrates as well and as easily.
Velodyne DD-18 or 15----fantastic integration-- Rel is good also, but not as good as Velodyne IMHO